SMPTE color bars is a type of television test pattern, and is most commonly used in countries where the NTSC video standard is dominant, such as in North America. The SMPTE refers to this test card as Engineering Guideline EG 1-1990.
In an SMPTE color bar image, the top two-thirds of the television picture contain seven vertical bars of 75% intensity. In order from left to right, the colors are white, yellow, cyan, green, magenta, red and blue. This sequence would show up on a waveform monitor as a staircase in luminance mode. Below the main set of seven bars is a castellation of blue, magenta, cyan and white boxes. When a television receiver is set to filter out all colors except for blue, these castellations, combined with the main set of color bars, are used to properly adjust the color controls, and would show up as four solid blue bars, with no visible distinction between the bars and the castellations, if the color controls are indeed adjusted properly.
The bottom section of the test pattern contains checks for proper white and black levels, as well as two sections that contain -I and +Q tests (see YIQ), that show up on a vectorscope as two short lines 90° apart. These are used to ensure that the television receiver properly decodes the 3.58 MHz color subcarrier portion of the signal.
These bars are half of the casual term "bars and tone." Typically, a television network, station or other originator of video programming transmits SMPTE color bars together with a continuous 1000 Hz audio tone ("bars and tone") before sending program material in order to assert ownership of the transmission line or medium, and so that receiving stations and intermediary telecommunications providers may adjust their equipment. Likewise, producers of television programs typically record "bars and tone" at the beginning of a videotape or other recording medium so that the playback equipment can be calibrated. Often, the name or identification of the TV station, other information such as a real-time clock, or another signal source is graphically superimposed over the bars.
